Chemistry laboratories play an essential role in the education of undergraduate Science, Technology, Engineering, and Mathematics (STEM) and non-STEM students. The extent of student learning in any educational environment depends largely on the effectiveness of the instructors. In chemistry laboratories at large universities, the instructors of record are typically graduate or undergraduate teaching assistants (TAs). Despite the importance of their role in the education of undergraduate students, TAs' instructional practices have been largely understudied outside specific reform efforts. In this study, we developed a segmented observation protocol, the Laboratory Observation Protocol for Undergraduate STEM (LOPUS), in order to characterize TAs' instructional styles in a General Chemistry laboratory curriculum. LOPUS captures both students' and TAs' behaviors every 2 min as well as initiators of verbal interactions and the nature of these verbal interactions (e.g., data analysis, explanation of concepts). Analyses of 19 videos collected from 15 TAs resulted in the identification of four instructional styles: the waiters, the busy bees, the observers, and the guides on-the-side. We found that students' behaviors were independent of these styles and limited to performing the laboratory activities, initiating conversation with TAs, and asking TAs questions. Interestingly, students rather than TAs were initiators of most verbal interactions, regardless of TAs' instructional styles. Finally, we found that the nature of TA−student verbal interactions was related to the nature of the laboratory activity (e.g., only following step-by-step instructions versus carrying out extensive data analysis). Implications of these findings for future research investigations and TA training are discussed.

Understanding resonance is essential to predict chemical reactivity and explain reaction mechanisms. Despite its importance in the organic curriculum, few studies have explored students’ difficulties with this concept and faculty’s instructional approaches to teaching it. The goals of this study are to address this gap in the literature by (1) employing an exploratory mixed-methods design to characterize students’ conceptual struggles with resonance and (2) exploring the relationship between students’ struggles and the instructional approach employed. Leveraging the results of a set of interviews with organic chemistry students, we distributed a survey to students in two different sections of a first-semester organic chemistry course at a research-intensive institution. We also conducted postinstruction interviews with the two instructors of the surveyed sections. Analysis of the 180 surveys collected indicates that students tended to focus on the features and processes of recognizing and drawing resonance structures when asked to explain the concept of resonance and mostly did not understand the relationship between resonance structures and the resonance hybrid. A comparison of the two sections showed a significant difference with one section having a better conceptual understanding of resonance than the other. Analysis of the instructional approaches demonstrated that the instructor of the section with higher conceptual understanding focused his instruction on the limitations of chemical representations, while the other instructor focused on the features and processes of recognizing and drawing resonance. This study highlights the need to help students develop metarepresentational competence as well as to better understand instructors’ instructional decisions.

Student learning in the classroom depends pre-eminently on the knowledge an instructor draws from when teaching a particular subject area to a particular group of students, also known as pedagogical content knowledge. While studies over the last decade have shed some light on the general pedagogical knowledge of science, technology, engineering and mathematics (STEM) instructors and their implementation of that knowledge in the classroom, the pedagogical content knowledge (PCK) of a STEM faculty is a largely overlooked area of inquiry. However, its investigation is critical in this era of instructional reforms, as studies have shown that PCK is essential for the effective implementation of active learning strategies. In this study, we conducted semi-structured interviews to probe the enacted pedagogical content knowledge (ePCK) of seven post-secondary organic chemistry instructors on the topic of resonance. Additionally, we administered an open-ended survey on resonance to students enrolled in these instructors' courses, to gauge their conceptual understanding. From the interviews, the instructors were assigned to one of four groups based on their ePCK of the resonance hybrid. Our findings do not conclusively support the notion that students develop a better conceptual understanding from instructors who hold a more comprehensive and integrated ePCK.